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Chapter 4: Tissues
A Tissue is…
a group of closely associated cells that perform related
functions and are similar in structure.
Four Basic Tissue Types and Basic Functions:
• 
• 
• 
• 
Epithelial tissue—covering (Chapters 4 and 5)
Connective tissue—support (Chapters 4, 5, 6, and 9)
Muscle tissue—movement (Chapters 10 and 11)
Nervous tissue—control (Chapters 12–16 and 25)
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Special Characteristics of Epithelia
Epithelial Tissue
•  Covers a body surface or lines a body cavity
•  Forms parts of most glands
•  Functions of epithelia
•  Protection
•  Diffusion
•  Absorption, secretion, and ion transport
•  Filtration
•  Forms slippery surfaces
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Special Characteristics of Epithelia
Cilia
•  Cellularity
•  Cells separated by minimal extracellular material
•  Specialized contacts
•  Cells joined by special junctions
•  Polarity
•  Cell regions of the apical surface differ from the basal surface
•  Supported by connective tissue underneath
•  Avascular but innervated
•  Epithelia receive nutrients from underlying connective tissue
•  Regeneration
•  Lost cells are quickly replaced by cell division
Narrow
extracellular
space
Cell junctions
Tight junction
Adhesive belt
Desmosome
Gap junction
Epithelium
Nerve ending
Connective
tissue
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How Epithelia is classified… 2 criteria:
Microvilli
Apical region of
an epithelial cell
Basal region
Basal
lamina
Basement
Reticular
membrane
fibers
Capillary
Figure 4.1
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Classifications of Epithelia
Apical surface
•  First name of tissue indicates number of cell layers:
Basal surface
•  Simple—one layer of cells on a basement membrane
•  Stratified—more than one layer of cells with basla
layer attached to basement membrane
•  Last name of tissue describes shape of cells on the
apical surface:
•  Squamous—cells are wider than tall (plate-like)
•  Cuboidal—cells are as wide as tall, like cubes
•  Columnar—cells are taller than they are wide, like
columns
Squamous
Simple
Apical surface
Cuboidal
Basal surface
Stratified
(a) Classification based on number
of cell layers
Columnar
(b) Classification based on cell shape
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Figure 4.2
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Simple Squamous Epithelium
Simple Cuboidal Epithelium
(a) Simple squamous epithelium
(b) Simple cuboidal epithelium
Description: Single layer of flattened
cells with disc-shaped central nuclei
and sparse cytoplasm; the simplest
of the epithelia.
Description: Single layer of
cubelike cells with large, spherical
central nuclei.
Simple
cuboidal
epithelial
cells
Air sacs of
lung tissue
Function: Allows passage of materials
by diffusion and filtration in sites where
protection is not important; secretes
lubricating substances in serosae.
Nuclei
of squamous
epithelial
cells
Location: Kidney glomeruli; air sacs
of lungs; lining of heart, blood vessels,
and lymphatic vessels; lining of ventral
body cavity (serosae).
Function: Secretion and absorption.
Basement
membrane
Location: Kidney tubules; ducts
and secretory portions of small
glands; ovary surface.
Connective
tissue
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (200×).
Photomicrograph: Simple cuboidal epithelium
in kidney tubules (430×).
Figure 4.3a
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Figure 4.3b
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Figure 4.3c Epithelial tissues.
Simple columnar epithelium
Simple Columnar Epithelium
Description: Single layer of tall
cells with round to oval nuclei;
some cells bear cilia; layer may
contain mucus-secreting
unicellular glands (goblet cells).
(c) Simple columnar epithelium
Description: Single layer of tall cells
with round to oval nuclei; some cells
bear cilia; layer may contain mucussecreting unicellular glands (goblet
cells).
Simple
columnar
epithelial
cell
Function: Absorption; secretion of
mucus, enzymes, and other substances;
ciliated type propels mucus (or
reproductive cells) by ciliary action.
Location: Nonciliated type lines most
of the digestive tract (stomach to anal
canal), gallbladder, and excretory ducts
of some glands; ciliated variety lines
small bronchi, uterine tubes, and some
regions of the uterus.
Basement
membrane
Photomicrograph: Simple columnar epithelium
of the stomach mucosa (1150×).
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Figure 4.3c
Microvilli
Goblet
cell
Simple
columnar
epithelial
cell
Function: Absorption; secretion
of mucus, enzymes, and other
substances; ciliated type propels
mucus (or reproductive cells) by
ciliary action.
Location: Nonciliated type lines
most of the digestive tract
(stomach to anal canal),
gallbladder, and excretory ducts
of some glands; ciliated variety
lines small bronchi,
uterine tubes,
and some
regions of
the uterus.
Basement
membrane
Photomicrograph: Simple columnar epithelium
of the small intestine (650×).
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Pseudostratified Columnar Epithelium
Pseudostratified Columnar Epithelium
•  Description
•  Function—secretion of mucus; propulsion of
mucus by cilia
•  Locations
• 
• 
• 
• 
All cells originate at basement membrane
Only tall cells reach the apical surface
May contain goblet cells and bear cilia
Nuclei lie at varying heights within cells
•  Gives false impression of stratification
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•  Nonciliated type
•  Ducts of male reproductive tubes
•  Ducts of large glands
•  Ciliated variety
•  Lines trachea and most of upper respiratory
tract
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Figure 4.3d Epithelial tissues.
Pseudostratified columnar epithelium
Description: Single layer of
cells of different heights, some
not reaching the free surface;
nuclei seen at different levels;
may contain mucus-secreting
goblet cells and bear cilia.
Cilia
Goblet
cell
(d) Pseudostratified columnar epithelium
Cilia
Mucus of
goblet cell
Description: Single layer of cells of
differing heights, some not reaching
the free surface; nuclei seen at different
levels; may contain mucus-secreting
goblet cells and bear cilia.
Pseudostratified
epithelial
layer
Function: Secretion, particularly
of mucus; propulsion of mucus
by ciliary action.
Pseudostratified
epithelial
layer
Function: Secretion, particularly of
mucus; propulsion of mucus by ciliary
action.
Location: Nonciliated type in
male’s sperm-carrying ducts and
ducts of large glands; ciliated
variety lines the trachea,
most of the upper respiratory
tract.
Trachea
Pseudostratified Ciliated Columnar
Epithelium(a type of simple epithelia)
Basement
membrane
Photomicrograph: Pseudostratified ciliated
columnar epithelium lining the human trachea
(780×).
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Location: Nonciliated type in male’s
sperm-carrying ducts and ducts of large
glands; ciliated variety lines the trachea,
most of the upper respiratory tract.
Photomicrograph: Pseudostratified ciliated
columnar epithelium lining the human trachea (780×).
Trachea
Figure 4.3d
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Stratified Epithelia
Stratified Squamous Epithelium
•  Properties
•  Description
• 
• 
• 
• 
Contain two or more layers of cells
Regenerate from below (basal layer)
Major role is protection
Named according to shape of cells at apical layer
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Stratified Squamous Epithelium
• 
• 
• 
Two types—keratinized and non-keratinized
•  Keratinized
•  Location—epidermis (superficial layer of skin)
•  Contains the protective protein keratin
•  Waterproof
•  Surface cells are dead and full of keratin
•  Non-keratinized
•  Forms moist lining of body openings
Function—Protects underlying tissues in areas subject to abrasion
Location
•  Keratinized—forms epidermis
•  Nonkeratinized—forms lining of mucous membranes
•  Esophagus
•  Mouth
•  Anus
•  Vagina
•  Urethra
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Basement
membrane
•  Many layers of cells are squamous in shape
•  Deeper layers of cells appear cuboidal or columnar
•  Thickest epithelial tissue
•  Adapted for protection from abrasion
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Stratified Squamous Epithelium
(e) Stratified squamous epithelium
Description: Thick membrane composed
of several cell layers; basal cells are
cuboidal or columnar and metabolically
active; surface cells are flattened
(squamous); in the keratinized type, the
surface cells are full of keratin and dead;
basal cells are active in mitosis and
produce the cells of the more superficial
layers.
Stratified
squamous
epithelium
Nuclei
Basement
membrane
Function: Protects underlying tissues
in areas subjected to abrasion.
Location: Nonkeratinized type forms the
moist linings of the esophagus, mouth,
and vagina; keratinized variety forms the
epidermis of the skin, a dry membrane.
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Connective
tissue
Photomicrograph: Stratified squamous epithelium
lining the esophagus (430×).
Figure 4.3e
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Stratified Cuboidal Epithelium
Stratified Columnar Epithelium
(g) Stratified columnar epithelium
(f) Stratified cuboidal epithelium
Description: Generally two
layers of cubelike cells.
Basement
membrane
Description: Several cell layers;
basal cells usually cuboidal;
superficial cells elongated
and columnar.
Basement
membrane
Cuboidal
epithelial
cells
Function: Protection
Function: Protection; secretion.
Location: Largest ducts of sweat
glands, mammary glands, and
salivary glands.
Duct
lumen
Photomicrograph: Stratified cuboidal epithelium forming
a salivary gland duct (285×).
Photomicrograph: Stratified columnar epithelium
lining of the male urethra (315×).
Urethra
Figure 4.3f
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Stratified
columnar
epithelium
Location: Rare in the body; small
amounts in male urethra and in large
ducts of some glands.
Underlying
connective
tissue
Figure 4.3g
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PowerPoint® Lecture Slides
prepared by
Leslie Hendon
University of Alabama,
Birmingham
Transitional Epithelium (a type of stratified [layed] epithelium)
(h) Transitional epithelium
Description: Resembles both
stratified squamous and stratified
cuboidal; basal cells cuboidal or
columnar; surface cells dome shaped
or squamous-like, depending on
degree of organ stretch.
CHAPTER
Part 1
Transitional
epithelium
Function: Stretches readily and
permits distension of urinary organ
by contained urine.
Location: Lines the ureters, bladder,
and part of the urethra.
Basement
membrane
Connective
tissue
Photomicrograph: Transitional epithelium lining the bladder,
relaxed state (390×); note the bulbous, or rounded, appearance
of the cells at the surface; these cells flatten and become
elongated when the bladder is filled with urine.
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Figure 4.3h
Glands (a special type of epithelium)…
2 general types: endocrine and exocrine.
•  Endocrine glands
•  Ductless glands that secrete directly into surrounding tissue fluid
•  Produce messenger molecules called hormones
•  Covered in detail in chapter 17
•  Exocrine glands
•  Ducts carry products of exocrine glands to epithelial surface
•  Include the following diverse glands
• 
• 
• 
• 
Mucus-secreting glands
Sweat and oil glands
Salivary glands
Liver and pancreas
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Unicellular Exocrine Glands (The Goblet Cell)
•  Goblet cells produce mucin
•  Mucin + water ! mucus
•  Protects and lubricates many internal body surfaces
•  Goblet cells are a unicellular exocrine gland
Multicellular Exocrine Glands
•  Have two basic parts:
•  Epithelium-walled duct
•  Secretory unit
•  Classified by structure of duct
•  Simple
•  Compound
•  Categorized by secretory unit
•  Tubular
•  Alveolar
•  Tubuloalveolar
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Goblet Cells– unicellular exocrine gland
Types of Multicellular Exocrine Glands
Microvilli
Secretory
vesicles
containing
mucin
Rough ER
Golgi
apparatus
Nucleus
(a)
(b)
Figure 4.4
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Figure 4.5
Lateral Surface Features—Cell Junctions
Lateral Surface Features—Cell Junctions
•  Factors binding epithelial cells together
•  Adhesion proteins link plasma membranes
of adjacent cells
•  Contours of adjacent cell membranes
•  Special cell junctions
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•  Tight junctions (zona occludens)—close off
intercellular space
•  Found at apical region of most epithelial
tissues types
•  Some proteins in plasma membrane of
adjacent cells are fused
•  Prevent certain molecules from passing
between cells of epithelial tissue
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Tight Junction
Lateral Surface Features—Cell Junctions
•  Adhesive belt junctions (zonula adherens)
—anchoring junction
•  Transmembrane linker proteins attach to
actin microfilaments of the cytoskeleton and
bind adjacent cells
•  With tight junctions, these linker proteins
form the tight junctional complex around
apical lateral borders of epithelial tissues
Interlocking
junctional
proteins
Intercellular
space
(a) Tight junctions: Impermeable junctions
prevent molecules from passing through
the intercellular space.
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Figure 4.6a
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Lateral Surface Features
Lateral Surface Features
•  Desmosomes—main junctions for binding
cells together
•  Desmosomes (continued)
•  Scattered along abutting sides of adjacent
cells
•  Cytoplasmic side of each plasma membrane
has a plaque
•  Plaques are joined by linker proteins
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•  Intermediate filaments extend across the
cytoplasm and anchor at desmosomes on
opposite side of the cell
•  Are common in cardiac muscle and epithelial
tissue
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Desmosome
Lateral Surface Features—Cell Junctions
Intercellular
space
•  Gap junctions—passageway between two
adjacent cells
Plaque
Intermediate
filament
(keratin)
•  These let small molecules move directly
between neighboring cells
•  Cells are connected by hollow cylinders of
protein
•  Function in intercellular communication
Linker
glycoproteins
(cadherins)
(b) Desmosomes: Anchoring junctions bind
adjacent cells together and help form an
internal tension-reducing network of fibers.
Figure 4.6b
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Gap Junction
Basal Feature: The Basal Lamina
Intercellular
space
•  Noncellular supporting sheet between the ET and the CT
deep to it
•  Consists of proteins secreted by ET cells
•  Functions
•  Acts as a selective filter, determining which molecules
from capillaries enter the epithelium
•  Acts as scaffolding along which regenerating ET cells
can migrate
•  Basal lamina and reticular layers of the underlying CT
deep to it form the basement membrane
Channel
between cells
(connexon)
(c) Gap junctions: Communicating junctions
allow ions and small molecules to pass
from one cell to the next for intercellular
communication.
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Figure 4.6c
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Epithelial Surface Features
Epithelial Surface Features
•  Apical surface features
•  Apical surface features
• 
•  Microvilli—fingerlike extensions of plasma
membrane
•  Abundant in ET of small intestine and
kidney
•  Maximize surface
area across which
Microvillus
small molecules
enter or leave
Actin
•  Act as stiff knobs
filaments
that resist abrasion
Figure 4.7
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A Cilium
Outer
microtubule
doublet
Central
microtubule
Dynein arms
Cross-linking
proteins inside
outer doublets
Radial spoke
Plasma
membrane
•  Cilia—whiplike, highly motile extensions of apical surface
membranes
•  Contain a core of microtubules held together by cross-linking
and radial proteins
•  Microtubules arranged in pairs called doublets
•  Movement is generated when adjacent doublets grip each
other with the motor protein dynein
•  Cilia originate as microtubules assemble around centrioles
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Connective Tissue
Power, or
propulsive,
stroke
The doublets
also have
attached motor
proteins, the
dynein arms.
The outer
microtubule
doublets and
the two central
microtubules
are held
together by
cross-linking
proteins and
radial spokes.
Recovery stroke, when
cilium is returning to
its initial position
•  Most diverse and abundant tissue
•  Main classes
1
2
3
4
5
6
7
(b) Phases of ciliary motion
• 
• 
• 
• 
Connective tissue proper
Cartilage
Bone tissue
Blood
•  Cells separated by a large amount of extracellular matrix
•  Extracellular matrix is composed of ground substance and
fibers
•  Common embryonic origin—mesenchyme
Layer of mucus
Cilium
Cell surface
Basal body
(centriole)
(a) Structure of a cilium
(c) Traveling wave created by the activity
of many cilia acting together propels
mucus across cell surfaces.
Figure 4.8
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Classes of Connective Tissue
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Structural Elements of Connective Tissue
(a) Embryonic connective tissue: mesenchyme
Description: Embryonic connective
tissue; gel-like ground substance
containing fibers; star-shaped
mesenchymal cells.
Function: Gives rise to all other
connective tissue types.
Mesenchymal
cell
Ground
substance
Location: Primarily in embryo.
Fibers
Photomicrograph: Mesenchymal tissue, an embryonic
connective tissue (600×); the clear-appearing background is
the fluid ground substance of the matrix; notice the fine,
sparse fibers.
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Figure 4.10a
•  Connective tissues differ in structural properties
•  Differences in types of cells
•  Differences in composition of extracellular matrix
(fibers and ground substance [dissolved or
suspended molecules]).
•  However, connective tissues all share structural
elements
•  Loose areolar connective tissue
•  This C.T. will illustrate connective tissue features:
Cells, Fibers, and Ground substance
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Structural Elements of Connective Tissue
•  Cells—primary cell type of connective tissue produces matrix
•  Fibroblasts
•  Make protein subunits
•  Secrete molecules that form the ground substance
•  Chondroblasts—secrete matrix in cartilage
•  Osteoblasts—secrete matrix in bone
•  Blood cells are an exception
•  Do not produce matrix
•  Areolar connective tissue contains
•  Fat cells
•  White blood cells
•  Mast cells
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Structural Elements of Connective Tissue
Structural Elements of Connective Tissue
•  Extracellular matrix is composed of fibers and ground
substance
•  Fibers function in support and have unique properties—
Types:
•  Collagen fibers—strongest; resist tension
•  Reticular fibers—bundles of special type of collagen
•  Cover and support structures
•  Elastic fibers—contain elastin
•  Recoil after stretching
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Structural Elements of Connective Tissue
Cell types
•  Ground substance
•  Is produced by primary cell type of the tissue
•  Is usually gel-like
•  Cushions and protects body structures (can be
“spongy”)
•  Holds tissue fluid
•  Blood is an exception
•  Plasma is not produced by blood cells
Macrophage
Extracellular
matrix
Ground substance
Fibers
Collagen fiber
Elastic fiber
Fibroblast
Reticular fiber
Lymphocyte
Fat cell
Capillary
Mast cell
Neutrophil
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Figure 4.9
Table 4.2 Comparison of Classes of Connective Tissues (1 of 2)
Connective Tissue Proper
•  Has two subclasses
•  Loose connective tissue
•  Areolar, adipose, and reticular
•  Dense connective tissue
•  Dense irregular, dense regular, and elastic
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Table 4.2 Comparison of Classes of Connective Tissues (2 of 2)
Areolar Connective Tissue—A Model
Connective Tissue
•  Areolar connective tissue
•  Underlies epithelial tissue
•  Surrounds small nerves and blood vessels
•  Has structures and functions shared by other
CT
•  Borders all other tissues in the body
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Major Functions of Connective Tissue
Areolar Connective Tissue
•  Structure of areolar connective tissue reflects
its functions
•  Fibers provide support
• 
• 
• 
• 
Support and binding of other tissues
Holding body fluids (interstitial fluid ! lymph)
Defending body against infection
Storing nutrients as fat
•  Three types of protein fibers in extracellular
matrix
•  Collagen fibers
•  Reticular fibers
•  Elastic fibers
•  Fibroblasts produce these fibers
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Areolar Connective Tissue
•  Description
•  Gel-like matrix with all three fiber types
•  Cells of areolar CT
•  Fibroblasts, macrophages, mast cells, and white blood cells
•  Function
•  Wraps and cushions organs
•  Holds and conveys tissue fluid (interstitial fluid)
•  Important role in inflammation
•  Locations
•  Widely distributed under epithelia
•  Packages organs
•  Surrounds capillaries
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Areolar Connective Tissue
(b) Connective tissue proper: loose connective tissue, areolar
Description: Gel-like matrix with all
three fiber types; cells: fibroblasts,
macrophages, mast cells, and some
white blood cells.
Function: Wraps and cushions organs;
its macrophages phagocytize bacteria;
plays important role in inflammation;
holds and conveys tissue fluid.
Location: Widely distributed under
epithelia of body, e.g., forms lamina
propria of mucous membranes;
packages organs; surrounds capillaries.
Epithelium
Elastic
fibers
Collagen
fibers
Fibroblast
nuclei
Photomicrograph: Areolar connective tissue, a soft packaging
tissue of the body (360×).
Lamina
propria
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Figure 4.10b
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Areolar Connective Tissue
Areolar Connective Tissue
•  Tissue fluid (interstitial fluid)
•  Main battlefield in fight against infection
•  Defenders gather at infection sites
•  Macrophages
•  Plasma cells
•  Mast cells
•  White blood cells
•  Neutrophils, lymphocytes, and eosinophils
•  Watery fluid occupying extracellular matrix
•  Tissue fluid derives from blood
•  Ground substance
•  Viscous, spongy part of extracellular matrix
•  Consists of sugar and protein molecules
•  Made and secreted by fibroblasts
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